Patent GB-649168-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B21B37/54
Filed: 1948-06-23
Abstract: 649,168. Automatic tension, speed, control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 23, 1948, No. 16864. Convention date, June 30, 1947. [Class 38 (iv)] [Also in Group XXXVII] A drive for a tandem mill comprises a plurality of mill motors, a separate main generator to supply each motor, and a regulating generator associated with each main generator controlling its output in accordance with the speed of its associated motor and a common variable reference voltage. Speed.-Motor 102 is maintained at a speed determined by a master generator 12 by supplying the motor armature from a main generator 103, the field of which is supplied by the master generator in series with a buck-boost control generator 114, in turn controlled by a regulating, generator 115, one winding 115c of which is excited in accordance with the difference between the output of the master generator 12 and the output of a tachometer generator 110 driven by the motor. An anti-hunting transformer 123 injects into the winding 115c a corrective voltage proportional to the rate of change of voltage of the control generator 114. The motor field is supplied from a field exciter 105. The arrangements for motors 202, 302 are similar. Tension; current.-The tension in the strip being wound on to reel 400 is maintained constant by varying the field excitation' of the motor 402 and by maintaining the armature current constant. The field is controlled by a rheostat 407 driven by a motor 445 supplied from a generator 447. The resultant field of this generator is the difference between the output voltage of a tachometer generator 337 (driven by the preceding mill motor 302) and the output voltage of the main generator 403, so that as the reel slows down due to the increasing diameter of the coil, the generator 447 energizes the motor 445 to increase the field excitation of the reel motor. Relays 449, 450 reverse the motor 445 at the end of reeling to quickly return the regulator 407 to its initial position. The armature current of motor 402, supplied from main generator 403, is controlled by a field 415d on the regulating generator 415 being energized according to the motor armature current. Generator 415 excites a control generator 414 which in turn excites the main generator. A tension control relay 446 reduces the excitation of generator 415 and hence reduces the output of main generator 403 to maintain a reduced value of tension in the strip when the mill is stopped or stalled. Acceleration compensation.-A generator 25 supplies a motor 22'which (under the control of push-buttons 32, 33) operates the field regulator 20 of the master generator 12. Since the voltage of generator 25 determines the rate at which the regulator is moved and hence the acceleration of the entire mill, an appropriate portion of this voltage is applied to one field 115f of the motor regulating generator 115 (and similarly for the other two mill motors) and to one field 415f of a regulating generator 415 associated with the reel motor 400 so as to compensate for the different inertias and various time constants of the machines. Taper tensioning.-The resultant of a reference voltage and a voltage proportional to the speed of the mill (derived from a taper tension generator 38 excited from the master generator 12) is applied to one winding 110d of the tachometer generator 110 via a rectifier 113 so that as the mill slows down and the voltage of generator 38 falls, winding 110d is energized to tend to decrease the speed of motor 102 and reduce the tension in the strip. Similar arrangements are applied to motors 202, 302. Manual controls.-Motor 102 is provided with forward and reverse inching push-buttons 130, 131 to connect the winding 115c of the regulating generator to fixed supply bars, and to disconnect the tapered tension winding of the tachometer generator 110, so as to effect slow running of the mill motor. Similar arrangements are provided for motors 202; 302 and 402. Threading and loop take-up.-To take up the loops provided between stands during threading, relays 224, 324, increase the speed of motors 202, 302, these relays being de-energized after a time delay by load responsive relays 233, 333. Overspeeding of reel motor 402 during threading is prevented by a winding 415e on the regulating generator 415 energized by the resultant of the outputs of tachometer generator 337 and tachometer generator 410. A rectifier 444 blocks the circuit during normal operation when the voltage of generator 410 falls below that of generator 337. Specification 649,169 is referred to.